1. Field of the Invention
The present invention relates to an automatic transmission and particularly to an assembling process for a Ravignawx type planetary gear train having stepped long pinions.
2. Description of the Prior Art
Generally, in the mechanism of this kind of a Ravignawx type planetary gear 1, as shown in FIG. 10, for example, there are provided coaxially an input shaft 2 and an output shaft 3. To the end of the input shaft 2 is fitted a rear sun gear 4, and into the input shaft 2 is inserted a front sun gear 5 through a clutch (not shown). Also, to the output shaft 3 is fitted a carrier 6 havaing a predetermined diameter, and this carrier 6 is provided with three pairs of support shafts 7, 8 in parallel at angular intervals of 120 degrees in the shifted phase around the output shaft 3. To this support shaft 7 is rotatably fitted a short pinion 10 meshing with the front sun gear 5 and a ring gear 9 which is coaxially provided in the outside periphery of the front sun gear 5. Also, to the support shaft 8 is rotatably fitted a long pinion 11 meshing with the short pinion 10 and the rear sun gear 4 commonly.
Recently, this long pinion 11 has been replaced, in view of the reduction gear ratio, with a stepped long pinion 15 comprising a long front gear 16 and a long rear gear 17, as shown in FIG. 1. In this case the long pinion 15 which is rotatably fitted to the shaft 8 of the carrier 6, the long front gear 16 is meshed with and connected to the front sun gear 5 and the ring gear 9 through the short pinion 10 and also the long rear gear 17 is meshed with and connected to the rear sun gear 4, as shown in FIG. 12(a) and FIG. 12(b).
In order to accomplish the theoretically proper mesh with this stepped long pinion 15, it is required to satisfy the following conditions:
The condition No. 1 is to select the number of teeth so that the number of teeth of each gear may be in the proper mesh. The formula to select the number of teeth is omitted here.
Next, the condition No. 2 is for the long front gear 16 and long rear gear 17 of the stepped long pinion 15 to be adjusted to the same phase at each center of the tooth width in each one of tooth grooves 16a, 17a FIG. 2(a) to control the relative position of both the gears 16, 17.
Further, as the condition No. 3 it is required to control the relative positions between the mutual long pinions 15 for assembling the stepped long pinions 15 which have satisfied the condition No. 2. For example, as shown in FIG. 13, where the phase-controlled tooth forms are applied with markings M, when the marking M1 is located at an angle of .phi.1=0 from the line a1 tying the center of No. 1 stepped long pinion 15A to the center P of the input shaft 2, No. 2 stepped long pinion 15B and No. 3 stepped long pinion 15C must be assembled so that the markings M2, M3 may be located respectively at an angle of .phi.2=-120 degrees (240 degrees) from the line a2 and at an angle of .phi.3=-240 degrees (120 degrees) from line a3. Incidentally, the plus sign represents the position clockwise from the lines a2, a3, and the minus sign counterclockwise from the same lines, and the calculation of those positions can be obtained by known formulas, but omitted.
If those three conditions are not satisfied, the gears can not be meshed theoretically and can not to be assembled. But in practice there are backlashes in the respective gears, so that in some cases the assembly can be performed even when the above-described three conditions are not satisfied. In those cases, however, there are problems in that the rotation of the gear is lacking in smoothness, the contact between the teeth becomes too tight, and defects such as pitching occurs. Especially, when the condition No. 3 was not satisfied, there was a problem of the failure in meshing, as shown in a circle mark in FIG. 14.